BackgroundCommon chronic conditions, such as heart disease and cancer, are associated with increased psychological distress, functional limitations and shortened life expectancy, but whether these diseases alter aspects of personality remains unclear.MethodTo examine whether the onset of heart disease, stroke, diabetes, cancer, hypertension, arthritis and respiratory disease is associated with subsequent changes in personality traits of the five-factor model, we pooled data from the Health and Retirement Study, the Midlife in the United States Survey, and the graduate and sibling samples of the Wisconsin Longitudinal Study for an individual-participant meta-analysis (total n = 17 493; mean age at baseline 55.8 years).ResultsAfter adjustment for age, we observed consistent decreases in extraversion [−0.25 T-scores per one disease; 95% confidence interval (CI) −0.40 to −0.10], emotional stability (−0.40, 95% CI −0.61 to −0.19), conscientiousness (−0.44, 95% CI −0.57 to −0.30) and openness to experience (−0.25, 95% CI −0.37 to −0.13) but not in agreeableness (−0.05, 95% CI −0.19 to 0.08) after the onset of chronic diseases. The onset of each additional chronic disease accelerated the average age-related personality change by 2.5 years in decreasing extraversion, 5.5 years in decreasing conscientiousness, and 1.6 years in decreasing openness to experience, and attenuated the increasing levels of emotional stability by 1.9 years. Co-morbid conditions were associated with larger changes than single diseases, suggesting a dose–response association between morbidity and personality change.ConclusionsThese results support the hypothesis that chronic diseases influence personality development in adulthood.